This document describes the Carrier 48N Packaged Heating/Cooling Units, which are self-contained, combination gas heating and electric cooling units designed for outdoor installation. They can be installed on a rooftop or a ground-level slab, with an accessory roof-mounting curb required for rooftop downflow applications. The 48N units comply with California's maximum oxides of nitrogen (Nox) emission regulations and are equipped with an energy-saving, automatic, intermittent electric spark ignition system, eliminating the need for a continuously burning pilot. They are manufactured with natural gas controls and are designed for a minimum continuous return air temperature of 60°F (dry bulb) or an intermittent operation down to 55°F (dry bulb), suitable for use with night setback thermostats.
Function Description:
The Carrier 48N units provide both heating and cooling for residential and light commercial applications. They are designed to be integrated into existing duct systems, provided these systems are properly sized to handle the required airflow. The units are factory-charged with R-22 refrigerant, simplifying installation to connecting gas supply, air ducts, high- and low-voltage wiring, condensate drain, and installing a field-supplied air filter. The heating section operates within a specified temperature rise range, and the cooling section is designed for optimal airflow to maintain comfort.
Important Technical Specifications:
The 48N units are design-certified by A.G.A. and C.G.A. and tested in accordance with ANSI Z21.47-1987, ARI Standard 210-81, and ARI Standard 270-84, among others. They are suitable for use with natural or LP (propane) gases with appropriate controls and orifices.
Key specifications include:
- Cooling Capacity: Ranges from 17,800 Btuh to 59,500 Btuh, depending on the model.
- Rated Cooling Airflow: Ranges from 600 cfm to 2000 cfm.
- External Static Pressure (Cooling): Typically 0.10 to 0.20 in. water.
- ARI Sound Rating: Ranges from 7.8 to 8.4.
- Rated Heating Input: Ranges from 40,000 cfm to 120,000 cfm.
- Output Capacity (Heating): Ranges from 31,000 Btuh to 96,000 Btuh.
- AFUE (%): 77.5% for most models.
- Recommended Minimum Field-Supplied Filter Size: Varies by model, with disposable types ranging from 288 sq in. to 960 sq in., and cleanable/high-capacity types from 192 sq in. to 640 sq in.
- Electrical: Available in 208/230-1, 208/230-3, and 460-3 voltage/phase configurations. Full load amps, maximum fuse size, and minimum wire sizing vary significantly by model.
- Gas Supply Pressure (Natural Gas): 5.0 to 13.6 in. wc (min/max).
- Gas Supply Pressure (Propane Gas): 11.0 to 13.0 in. wc (min/max).
- Manifold Pressure (Natural Gas): 3.5 in. wc.
- Manifold Pressure (Propane Gas): 10.5 in. wc (12.5 in. wc for some 100,000 Btuh models).
- Refrigerant: R-22.
Usage Features:
- Installation Flexibility: Can be installed on rooftops or ground-level slabs.
- Duct Connections: Features duct flanges on the side and bottom for supply and return air. Proper panel removal is required for side or bottom discharge.
- Electrical Connections: Requires a separate electrical service with a field-supplied, waterproof, fused disconnect switch. Low-voltage control wiring connects to a room thermostat.
- Gas Piping: Requires a separate gas supply line from the meter to the heating section, with a sediment trap installed in the riser.
- Condensate Disposal: Uses a 3/4-in. NPT drain fitting, requiring a 2-in. trap for proper drainage.
- Venting: A vent-cap assembly is included and must be installed to ensure proper venting.
- Blower Motor: Direct-drive for 018-048 size units, belt-drive for 060 size units. Blower speed adjustments are possible for 208/230V direct-drive units.
- Safety Controls: Includes a manual reset circuit breaker, limit switch (LS), auxiliary limit switch (ALS), and fusible link (FL) to prevent overheating and ensure safe operation.
- Refrigerant Charge: Units are factory-charged. Adjustments are only required if a leak is suspected, based on superheat measurements.
Maintenance Features:
- Regular Inspections: Recommended annual inspection by a qualified service person.
- Air Filter: Inspect monthly and clean or replace when necessary. Recommended filter sizes are provided.
- Cooling Coil, Drain Pan, and Condensate Drain: Inspect and clean each cooling season.
- Blower Motor and Wheel: Inspect for cleanliness and check lubrication each heating and cooling season. Lubricate the motor every 5 years for intermittent use or every 2 years for continuous use.
- Electrical Connections: Check for tightness and proper operation each heating and cooling season.
- Heating Section: Inspect and clean before each heating season. Includes procedures for cleaning heat exchanger cells and burner assembly.
- Pilot: Inspect and clean at the beginning of each heating season, ensuring proper flame impingement on the flame sensor and correct spark gap.
- Condenser Coil: Inspect and clean annually, including straightening bent fins and removing obstructions.
- Condenser Fan: Inspect blades for cracks or bends annually, ensuring proper clearance and position on the motor shaft.
- Metering Device: Piston-type metering device. Procedures for checking, cleaning, and replacing the piston are provided, requiring refrigerant removal.
- Liquid Line Strainer: Made of wire mesh, located on the liquid line inlet side. Removal involves threading a screw into the strainer and pulling it out.
- Unit Top Removal: Detailed instructions for safe removal of the unit top for maintenance, emphasizing care to avoid damaging fan motor leads.
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